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Wed, 4 Mar 2026 02:37:26 -0800 From: Akhil R To: CC: , , , , , , , , , , , , , Subject: Re: [PATCH v2 1/9] dt-bindings: dma: nvidia,tegra186-gpc-dma: Add iommu-map property Date: Wed, 4 Mar 2026 16:07:25 +0530 Message-ID: <20260304103725.64228-1-akhilrajeev@nvidia.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <361e0146-c5af-4f16-a946-14d1df85f99b@nvidia.com> References: <361e0146-c5af-4f16-a946-14d1df85f99b@nvidia.com> Precedence: bulk X-Mailing-List: linux-tegra@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH3PEPF00000014:EE_|DS0PR12MB7875:EE_ X-MS-Office365-Filtering-Correlation-Id: f461025a-e65c-4cdc-bcc9-08de79da14ca X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|36860700016|1800799024|376014|7416014; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:216.228.117.161;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge2.nvidia.com;CAT:NONE;SFS:(13230040)(82310400026)(36860700016)(1800799024)(376014)(7416014);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: yx8CbQbzddXlgirXIr48l4GOz/wNtvY812Wlb5r+IXZ8BvXWZ6cC+SDgCt+onmmN6JooyDmnx3Gh9wWsOtpvv5OHpglxoLitPHJNhfNvQFX4P384nQXLOuqOpoLTcp5ZMVOAY1XGOn5rhS3YDW6VzjqdVjhyQrnndmt9Pe1SYc1bkY8GWg3mfy6szqG3hTjqUjVnWHFkKn5iz0VfEDfhFwMKncJo/Nh+2ogMRcPG6GHrCofk7JvJqG7o990PlzERfgsw5jXTPUKaT9BkCG8KITicEFB4ULMI4zPnpscJzhAaRG2lpZNBnmqQPI27vxnGZYYj/gMbHVhT+r5ZwUVEbtzMnfmsIpxqQRSycOiaAmeYZ7VdxlZHM4mD62CKfdNyqsBmGdsb72cq5mzVxpyMxE+OUiPsoYGsoYVoAB8mXG5Qp29zGAXyEilmftYk6v8k X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 Mar 2026 10:37:49.0136 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: f461025a-e65c-4cdc-bcc9-08de79da14ca X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CH3PEPF00000014.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR12MB7875 On Tue, 3 Mar 2026 17:34:00 +0000, Jon Hunter wrote: > On 03/03/2026 17:14, Akhil R wrote: >> On Tue, 3 Mar 2026 13:09:00 +0000, Jon Hunter wrote: >>> On 03/03/2026 08:40, Akhil R wrote: >>> >>> ... >>> >>>>> Why is this flexible? If it is, means usually items are distinctive, so >>>>> I would expect defining/listing them. If they are not distinctive, >>>>> commit msg is incorrect. If the list is as simple as 1-to-1 channel >>>>> mapping, just add it in the description how they are ordered. >>>> >>>> Yes, it is a 1-to-1 channel mapping to an IOMMU ID. The intent of making >>>> it flexible is to allow non-consecutive IOMMU ID assignments as well. >>>> This is particularly needed in virtualised environments where the >>>> hypervisor may reserve certain stream IDs, and the guest VM can map only >>>> the permitted ones. Shall I add a description here mentioning this >>>> use-case? >>> >>> Isn't this already handled by the 'dma-channel-mask' property? The >>> driver will skip over any channels that are not in specified by the mask. >> >> dma-channel-mask would not help if a channel is exposed, and the >> corresponding IOMMU ID is not exposed. For instance say channel 15 is > available for a VM, but not the stream ID 0x80f. > > Is that a valid configuration? Above we said it is a 1-to-1 mapping > which would imply the mapping is always constant. Ie. same channels maps > to name SID. Is that not the case? I think the hypervisor configuration can determinte which stream IDs are assigned to each VM, so the mapping can vary across platforms. By 1-to-1, I meant that each channel maps to one IOMMU ID, but the specific IDs themselves may not be fixed. If we prefer a constant mapping instead, we could document that only IDs in the range 0x801 to 0x81f should be allocated to a Linux VM. Happy to go either way. Let me know your thoughts. Regards, Akhil